PSL Chemical Biology Symposia: The Increasing Impact of Chemistry in Life Sciences

This symposium is the 6th Paris Sciences & Lettres (PSL) Chemical Biology meeting (2015, 2016, 2019, 2023, 2024, 2025) being held at Institut Curie. This initiative originally started in 2013 at Institut de Chimie des Substances Naturelles (ICSN) in Gif-sur-Yvette and was mostly focused on organic synthesis. It was then exported at Institut Curie to cover a larger scope, before becoming the official French Chemical Biology meeting. This year, around 200 participants had the opportunity to meet world leaders in chemistry and biology who described their latest innovations and future trends covering topics as diverse as prebiotic chemistry, activity-based protein profiling, high-resolution cell imaging, nanotechnologies, bio-orthogonal chemistry, metal ion signaling, ferroptosis, and biocatalysis.

Topological phase locking in stochastic oscillators

The dynamics of many nanoscale biological and synthetic systems such as enzymes and molecular motors are activated by thermal noise, and driven out-of-equilibrium by local energy dissipation. Because the energies dissipated in these systems are comparable to the thermal energy, one would generally expect their dynamics to be highly stochastic. Here, by studying a thermodynamically-consistent model of two coupled noise-activated oscillators, we show that this is not always the case. Thanks to a novel phenomenon that we term topological phase locking (TPL), the coupled dynamics become quasi-deterministic, resulting in a greatly enhanced average speed of the oscillators. TPL is characterized by the emergence of a band of periodic orbits that form a torus knot in phase space, along which the two oscillators advance in rational multiples of each other. The effectively conservative dynamics along this band coexists with the basin of attraction of the dissipative fixed point. We further show that TPL arises as a result of a complex, infinite hierarchy of global bifurcations. Our results have implications for understanding the dynamics of a wide range of systems, from biological enzymes and molecular motors to engineered nanoscale electronic, optical, or mechanical oscillators.

Metal-free iodosulfonylation of alkynes to access (E)-β-iodovinyl sulfones in water

With the escalating concerns regarding environmental pollution caused by organic solvents, chemists are increasingly focusing on conducting organic reactions in water, nature's chosen solvent for chemical synthesis. Herein, the development of metal-free iodosulfonylation of alkynes with p-toluenesulfonyl cyanide and NIS for the synthesis of (E)-β-iodovinyl sulfones in water is reported. This reaction gives the desired products in good to excellent yields with high regio- and stereoselectivity by using water as a green solvent at room temperature. This reaction could be readily scaled up, and synthetic application was also studied.

Hydrogen Bonding-Induced Multicolor and Thermochromic Emissions of Triphenylamines

The fluorescence tuning of stimuli-responsive materials is crucial but challenging. The deep understanding of thermal induced fluorescence change, however, has rarely been conducted. Herein, the thermochromic emission of a triphenylamine (TPA) derivative (1), with one acetyl and two 1-hydroxy-1-methylethyl units on each o-phenyl group around the nitrogen atom, has been investigated. Upon heating, the bright blue-emitting solid 1 turns to a strong green-emitting liquid. Moreover, 1 is green emissive in ethanol but blue emissive with high absolute quantum yields in dimethyl sulfoxide (DMSO). Another TPA derivative (2) is green emitting. X-ray crystallography studies reveal that the strong solid-state fluorescence arises from a rigid pyramidal structure around central nitrogen of 1, due to the OH•••OH, OH•••O = C hydrogen bonding interactions. Comparatively, 2 has a planar configuration of three C─N bonds around central nitrogen atom. This work will provide a new route for constructing multiemission materials using unimolecular platforms.

Strain Energy Induced Rotary Speed Acceleration in a Light-Driven Molecular Motor

Light-driven molecular motors based on overcrowded alkenes represent a major type of molecular machines that are able to rotate unidirectionally. The regulation of the rotary speed without altering the core structure of a motor is crucial and remains a major challenge. In the present study, we reported that the rotary speed of molecular motors can be significantly enhanced by harnessing the strain energy of cycloparaphenylene (CPP). A series of molecular motors incorporated in CPP with varying sizes were synthesized, and their photochemical and thermal isomerization behaviors were meticulously examined using UV-vis and 1H NMR spectroscopy. The remarkable increase of the acceleration effect of the rotary speed with decreasing macrocycle sizes, up to 389-fold, can be attributed to the strain energy induced bending in the stator part, which reduces steric hindrance in the "fjord region" of the molecule, supported by a detailed computational study employing density functional theory. This work provides systematic insight into the behavior of molecular motors under strain energy, thereby paving the way for the application of motor-incorporating CPPs as a general strategy to accelerate the rotary speed of molecular motors.

Light-Triggered Reversible Helicity Switching of a Rotor by a Photo-Responsive Plier

Controlling synchronized motion and transmission of molecular motion to a remotely located guest is not trivial. Here, we demonstrate a light-triggered, scissor-like conformational change in a molecular plier to reversibly alter the conformation and helical chirality of a noncovalently bound rotor. The plier comprises three building blocks: an azobenzene unit that controls the open-close motion of the plier upon light-activated isomerization from E to Z, a BINOL unit that serves as both a hinge and a chiral inducer and two pyridine moieties that can form a complex with the rotor guest. The light-induced conformational alteration of the plier was unequivocally demonstrated by 1H NMR, UV-Vis, and CD spectroscopy. The open-close motion of the plier was translated to the rotor via a 1 : 1 host-guest complex. Indeed, CD spectroscopy, NMR spectroscopy, thermal back isomerization studies, and molecular modelling confirm that the light-triggered conformational alterations of the plier can induce mechanical twisting and helicity switching in the rotor.

Algorithm in chemistry: molecular logic gate-based data protection

Data security is crucial for safeguarding the integrity, authenticity, and confidentiality of documents, currency, merchant labels, and other paper-based assets, which sequentially has a profound impact on personal privacy and even national security. High-security-level logic data protection paradigms are typically limited to software (digital circuits) and rarely applied to physical devices using stimuli-responsive materials (SRMs). The main reason is that most SRMs lack programmable and controllable switching behaviors. Traditional SRMs usually produce static, singular, and highly predictable signals in response to stimuli, restricting them to simple "BUFFER" or "INVERT" logic operations with a low security level. However, recent advancements in SRMs have collectively enabled dynamic, multidimensional, and less predictable output signals under external stimuli. This breakthrough paves the way for sophisticated encryption and anti-counterfeiting hardware based on SRMs with complicated logic operations and algorithms. This review focuses on SRM-based data protection, emphasizing the integration of intricate logic and algorithms in SRM-constructed hardware, rather than chemical or material structural evolutions. It also discusses current challenges and explores the future directions of the field-such as combining SRMs with artificial intelligence (AI). This review fills a gap in the existing literature and represents a pioneering step into the uncharted territory of SRM-based encryption and anti-counterfeiting technologies.

Electric field-driven dual-rotation in molecular motors: insights from molecular dynamics simulations

Understanding the interaction between molecular motors and their environment is crucial for their practical applications. In this study, we utilized classical molecular dynamics simulations to investigate the dynamic behavior of molecular motors in solvents and their response to external electric fields. By modulating the external electric field in conjunction with the charge state of the molecular motors, the rotational direction of the molecular motors could be tuned.

DNA photofluids show life-like motion

As active matter, cells exhibit non-equilibrium structures and behaviours such as reconfiguration, motility and division. These capabilities arise from the collective action of biomolecular machines continuously converting photoenergy or chemical energy into mechanical energy. Constructing similar dynamic processes in vitro presents opportunities for developing life-like intelligent soft materials. Here we report an active fluid formed from the liquid-liquid phase separation of photoresponsive DNA nanomachines. The photofluids can orchestrate and amplify nanoscale mechanical movements by orders of magnitude to produce macroscopic cell-like behaviours including elongation, division and rotation. We identify two dissipative processes in the DNA droplets, photoalignment and photofibrillation, which are crucial for harnessing stochastic molecular motions cooperatively. Our results demonstrate an active liquid molecular system that consumes photoenergy to create ordered out-of-equilibrium structures and behaviours. This system may help elucidate the physical principles underlying cooperative motion in active matter and pave the way for developing programmable interactive materials.

Gas-phase, conformer-specific infrared spectra of 3-chlorophenol and 3-fluorophenol

Conformational isomerism of phenol derivatives has been a subject of extensive spectroscopic study. Combining the capabilities of the widely tuneable infrared free-electron laser FELIX with molecular beam technologies allows for revisiting existing data and gaining additional insights into far-IR spectroscopy of halogenated phenols. Here we present conformer-resolved infrared spectra of the syn and anti conformers of 3-chlorophenol and 3-fluorophenol recorded via IR-UV ion-dip spectroscopy. The experimental work is complemented by density functional theory calculations to aid in assignment of the observed bands. The experimental spectra for the two conformers of each molecule show overall a great similarity, but also include some distinct conformer-specific bands in the spectral range investigated. Our spectra confirm previously reported OH torsional mode frequencies for the syn and anti conformers of 3-chlorophenol (3CP) at 315 cm-1, (Manocha et al., J. Phys. Chem., 1973, 77, 2094) but reverse their assignment of the 311 and 319 cm-1 bands for 3-fluorophenol. 1D torsional mode calculations were performed for 3CP to help assign possible OH torsion overtones.

Directional Macrocycle Transport, Release, and Recapture Enabled by a Rotaxane Transporter

A transporter for a directional macrocycle transport, release, and recapture was constructed. This was achieved using a rotaxane featuring a dibenzo-24-crown-8 macrocycle, dibenzylammonium (DBA)/methyl triazolium (MTA) stations on the thread and anthracene/triisopropylsilyl-acetylene stoppers, respectively. In the protonated rotaxane, the macrocycle primarily resides on the DBA station, followed by directional shuttling to the MTA station upon treatment with base. Addition of fluoride as an additional chemical input cleaves the triisopropylsilyl stopper, leading to release of the macrocycle and the half-thread into solution. The released macrocycle can be recaptured by protonation, and the mechanical bond can be reestablished via CuAAC click reaction, enabled by the terminal acetylene unit on the half-thread. This generates an elongated second-generation rotaxane transporter, which was used for a second cycle of directional macrocycle transport and release, proving the possibility of an iterative operation of the rotaxane-transporter in this molecular design.

Metareview: a survey of active matter reviews

In the past years, the amount of research on active matter has grown extremely rapidly, a fact that is reflected in particular by the existence of more than 1000 reviews on this topic. Moreover, the field has become very diverse, ranging from theoretical studies of the statistical mechanics of active particles to applied work on medical applications of microrobots and from biological systems to artificial swimmers. This makes it very difficult to get an overview over the field as a whole. Here, we provide such an overview in the form of a metareview article that surveys the existing review articles and books on active matter. Thereby, this article provides a useful starting point for finding literature about a specific topic.

Photoswitchable Topological Regulation of Covalent Macrocycles, Molecular Recognition, and Interlocked Structures

Macrocycles represent one important class of functional molecules, and dynamic macrocycles with the potential of cleavability, adaptability, and topological conversion are challenging. Herein we report photoswitchable allosteric and topological control of dynamic covalent macrocycles and further the use in guest binding and mechanically interlocked molecules. The manipulation of competing ring-chain equilibria and bond formation/scission within reaction systems enabled light-induced structural regulation over dithioacetal and thioacetal dynamic bonds, accordingly realizing bidirectional switching between crown ether-like covalent macrocycles and their linear counterparts. The on-demand photoswitchable topological transformation of macrocycles further allowed guest recognition/release exhibiting controllable binding affinity and selectivity. To showcase the capability light-triggered assembly/disassembly of diverse mechanically interlocked structures, such as rotaxanes and catenanes, was achieved. The realization of photoswitchable topological conversion of covalent macrocycles, which has been rarely reported before, demonstrates the potential of light-triggered reactivity control and structural reconfiguration for enhanced complexity and sophisticated function. The strategies and results should be appealing to endeavors in molecular recognition, dynamic assemblies, molecular machines, and intelligent materials.

General strategy for boosting the performance of speed-tunable rotary molecular motors with visible light

Light-driven molecular rotary motors perform chirality-controlled unidirectional rotations fueled by light and heat. This unique function renders them appealing for the construction of dynamic molecular systems, actuating materials, and molecular machines. Achieving a combination of high photoefficiency, visible-light responsiveness, synthetic accessibility, and easy tuning of dynamic properties within a single scaffold is critical for these applications but remains a longstanding challenge. Herein, a series of highly photoefficient visible-light-responsive molecular motors (MMs), featuring various rotary speeds, was obtained by a convenient one-step formylation of their parent motors. This strategy greatly improves all aspects of the performance of MMs-red-shifted wavelengths of excitation, high photoisomerization quantum yields, and high photostationary state distributions of isomers-beyond the state-of-the-art light-responsive MM systems. The development of this late-stage functionalization strategy of MMs opens avenues for the construction of high-performance molecular machines and devices for applications in materials science and biological systems, representing a major advance in the synthetic toolbox of molecular machines.

Computational Study on the Dynamics of a Bis(benzoxazole)-Based Overcrowded Alkene

Understanding and controlling molecular motions is of pivotal importance for designing molecular machinery and functional molecular systems, capable of performing complex tasks. Herein, we report a comprehensive theoretical study to elucidate the dynamic behavior of a bis(benzoxazole)-based overcrowded alkene displaying several coupled and uncoupled molecular motions. The benzoxazole moieties give rise to 4 different stable conformers that interconvert through single-bond rotations. By performing excited- and ground-state molecular dynamics simulations, DFT calculations, and NMR studies, we found that the photochemical E-Z isomerization of the central double bond of each stable conformer is directional and leads to a mixture of metastable isomers. This transformation is analogous to the classical Feringa-type molecular motors, with the notable difference that, during the photochemical isomerization and the subsequent thermal helix inversion (THI) steps, multiple possible pathways take place that involve single-bond rotations that can be both coupled and uncoupled to the rotation of the naphthyl half of the molecule.

Quantum-Classical Simulations Reveal the Photoisomerization Mechanism of a Prototypical First-Generation Molecular Motor

Light-driven molecular rotary motors convert the energy of absorbed light into unidirectional rotational motion and are key components in the design of molecular machines. The archetypal class of light-driven rotary motors is chiral overcrowded alkenes, where the rotational movement is achieved through consecutive cis-trans photoisomerization reactions and thermal helix inversion steps. While the thermal steps have been rather well understood by now, our understanding of the photoisomerization reactions of overcrowded alkene-based motors still misses key points that would explain the striking differences in operation efficiency of the known systems. Here, we employ quantum-chemical calculations and nonadiabatic molecular dynamics simulations to investigate the excited-state decay and photoisomerization mechanism in a prototypical alkene-based first-generation rotary motor. We show that the initially excited bright state undergoes an ultrafast relaxation to multiple excited-state minima separated by low energy barriers and reveal a slow picosecond-timescale decay to the ground state, which only occurs from a largely twisted dark excited-state minimum, far from any conical-intersection point. Additionally, we attribute the origin of the high yields of forward photoisomerization in our investigated motor to the favorable topography of the ground-state potential energy surface, which is controlled by the conformation of the central cyclopentene rings.

Reversible Isomerization of Stiff-Stilbene by an Oriented External Electric Field

Understanding and effectively controlling molecular conformational changes are essential for developing responsive and dynamic molecular systems. Here, we report that an oriented external electric field (OEEF) is an effective catalyst for the cis-trans isomerization of stiff-stilbene, a key component of overcrowded alkene-based rotary motors. This reversible isomerization occurs under ambient conditions, is free from side reactions, and has been verified using ultraperformance liquid chromatography and UV-vis absorption spectroscopy. Low electric field promotes cis-to-trans conversion, and high electric field enables the reverse trans-to-cis process, demonstrating the precise reaction control through electric field manipulation. Density functional theory calculations reveal the mechanism of the electric-field-catalyzed cis-trans carbon-carbon double bond isomerization. Our findings provide a novel perspective on constructing OEEF-catalyzed, reversible molecular systems and pave the way for fully electrically driven artificial molecular machines.

Coupling Rotary Motion to Helicene Inversion within a Molecular Motor

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded-alkene second-generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6-step cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In-depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems.

Rational engineering of DNA-nanoparticle motor with high speed and processivity comparable to motor proteins

DNA-nanoparticle motor is a burnt-bridge Brownian ratchet moving on RNA-modified surface driven by Ribonuclease H (RNase H), and one of the fastest nanoscale artificial motors. However, its speed is still much lower than those of motor proteins. Here we resolve elementary processes of motion and reveal long pauses caused by slow RNase H binding are the bottleneck. As RNase H concentration ([RNase H]) increases, pause lengths shorten from ~70 s to ~0.2 s, while step sizes (displacements between two consecutive pauses) are constant ( ~ 20 nm). At high [RNase H], speed reaches ~100 nm s-1, however, processivity (total number of steps before detachment), run-length, and unidirectionality largely decrease. A geometry-based kinetic simulation reveals switching of bottleneck from RNase H binding to DNA/RNA hybridization at high [RNase H], and trade-off mechanism between speed and other performances. An engineered motor with 3.8-times larger DNA/RNA hybridization rate simultaneously achieves 30 nm s-1 speed, 200 processivity, and 3 μm run-length comparable to motor proteins.

A Cost-Effective Computational Strategy for the Electronic Layout Characterization of a Second Generation Light-Driven Molecular Rotary Motor in Solution

Light-driven molecular rotary motors are nanometric machines able to convert light into unidirectional motions. Several types of molecular motors have been developed to better respond to light stimuli, opening new avenues for developing smart materials ranging from nanomedicine to robotics. They have great importance in the scientific research across various disciplines, but a detailed comprehension of the underlying ultrafast photophysics immediately after photo-excitation, that is, Franck-Condon region characterization, is not fully achieved yet. For this aim, it is first required to rely on an accurate description at ab initio level of the system in this potential energy region before performing any further step, that is, dynamics. Thus, we present an extensive investigation aimed at accurately describing the electronic structure of low-lying electronic states (electronic layout) of a molecular rotor in the Franck-Condon region, belonging to the class of overcrowded alkenes: 9-(2-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-ylidene)-9H-fluorene. This system was chosen since its photophysics is very interesting for a more general understanding of similar compounds used as molecular rotors, where low-lying electronic states can be found (whose energetic interplay is crucial in the dynamics) and where the presence of different substituents can tune the HOMO-LUMO gap. For this scope, we employed different theory levels within the time-dependent density functional theory framework, presenting also a careful comparison adopting very accurate post Hartree-Fock methods and characterizing also the different conformations involved in the photocycle. Effects on the electronic layout of different functionals, basis sets, environment descriptions, and the role of the dispersion correction were all analyzed in detail. In particular, a careful treatment of the solvent effects was here considered in depth, showing how the implicit solvent description can be accurate for excited states in the Franck-Condon region by testing both linear-response and state-specific formalisms. As main results, we chose two cost-effective (accurate but relatively cheap) theory levels for the ground and excited state descriptions, and we also verified how choosing these different levels of theory can influence the curvature of the potential via a frequency analysis of the normal modes of vibrations active in the Raman spectrum. This theoretical survey is a crucial step towards a feasible characterization of the early stage of excited states in solution during photoisomerization processes wherein multiple electronic states might be populated upon the light radiation, leading to a future molecular-level interpretation of time-resolved spectroscopies.

Bidirectional Molecular Motors by Controlling Threading and Dethreading Pathways of a Linked Rotaxane

Artificial molecular motors have been presented as models for biological molecular motors. In contrast to the conventional artificial molecular motors that rely on covalent bond rotation, molecular motors with mechanically interlocked molecules (MIMs) have attracted considerable attention owing to their ability to generate significant rotational motion by dynamically shuttling macrocyclic components. The topology of MIM-type rotational molecular motors is currently limited to catenane structures, which require intricate synthetic procedures that typically produce a low synthetic yield. In this study, we develop a novel class of MIM-type molecular motors with a rotaxane-type topology. The switching of the threading/dethreading pathways of the linked rotaxane by protecting/deprotecting the bulky stopper group and changing the solvent polarity enables a net unidirectional rotation of the molecular motor. The threading/dethreading reaction rates were quantitatively evaluated through detailed spectroscopic investigations. Repeated net unidirectional rotation and switching of the direction of rotation were also achieved. Our findings demonstrate that linked rotaxanes can serve as MIM-type molecular motors with reversible rotational direction controlled by threading/dethreading reactions. These motors hold potential as components of molecular machinery.

Artificial molecular motors in biological applications

Molecular motors are the cornerstone for the maintenance of living systems and mediate almost all fundamental processes involved in cellular trafficking. The intricate mechanisms underlying natural molecular motors have been elucidated in detail, inspiring researchers in various fields to construct artificial systems with multi-domain applications. This review summarises the characteristics of molecular motors, biomimetic approaches for their design and operation, and recent biological applications.

Designing a visible light-mediated double photoswitch: a combination of biradical and azobenzene structural motifs that can be switched independently

A new molecular switch is presented that combines both biradical and azobenzene motifs to perform visible light-induced constitutional and stereo-isomerisation within the same molecule. The insertion of isonitrile-functionalised azobenzenes into the four-membered biradical [˙P(μ-NTer)2P˙] (1), yielding a phosphorus-centred cyclopentane-1,3-diyl (E-4B and E-5B), represents a straightforward method to generate the desired double switches (E-4B and E-5B) in excellent yields (>90%). The switching properties are demonstrated for the fluorinated species E-5B and, interestingly, can occur either stepwise or simultaneously, depending on the order in which the sample is irradiated with red and/or green light. All possible isomerisation reactions, i.e., housane formation in the phosphorus-centred cyclopentane-1,3-diyl fragment and E/Z isomerisation at the azobenzene, can be switched by irradiation and the reaction products E-5H, Z-5H and Z-5B (when performing the thermal reverse reaction in the dark) are identified using 19F{1H} and 31P{1H} NMR spectroscopy. Results from quantum chemical calculations contribute to the understanding and visualisation of the different isomers of each of the observed compounds (E-5B, E-5H, Z-5H, and Z-5B) caused by the unique structure of the double switches.

A Multiresponsive Ferrocene-Based Chiral Overcrowded Alkene Twisting Liquid Crystals

The reversible modulation of chirality has gained significant attention not only for fundamental stereochemical studies but also for numerous applications ranging from liquid crystals (LCs) to molecular motors and machines. This requires the construction of switchable molecules with (multiple) chiral elements in a highly enantioselective manner, which is often a significant synthetic challenge. Here, we show that the dimerization of an easily accessible enantiopure planar chiral ferrocene-indanone building block affords a multi-stimuli-responsive dimer (FcD) with pre-determined double bond geometry, helical chirality, and relative orientation of the two ferrocene motifs in high yield. This intrinsically planar chiral switch can not only undergo thermal or photochemical E/Z isomerization but can also be reversibly and quantitatively oxidized to both a monocationic and a dicationic state which is associated with significant changes in its (chir)optical properties. Specifically, FcD acts as a chiral dopant for cholesteric LCs with a helical twisting power (HTP) of 13 μm-1 which, upon oxidation, drops to near zero, resulting in an unprecedently large redox-tuning of the LC reflection color by up to 84 nm. Due to the straightforward stereoselective synthesis, FcD, and related chiral switches, are envisioned to be powerful building blocks for multi-stimuli-responsive molecular machines and in LC-based materials.

Multimodal Molecular Motion in the Rotaxanes and Catenanes Incorporating Flexible Calix[n]phyrin Stations

The synthesis of [2]rotaxanes stoppered with one or two dipyrromethane groups has opened a route for the construction of mechanically interlocked molecules incorporating various porphyrinoid stations. The exploitation of those precursors allowed the creation of [3]rotaxanes and [2]catenanes based on the calix[4]phyrin motif, presenting intriguing molecular dynamics. The intrinsic flexibility of the porphyrinoid allowed the introduction of a new type of molecular motion within the rotaxanes, termed fluttering. The latter involved a bending of the axle, interconverting two angular-shaped stereoisomers of the rotaxane through a planarised transition state. Simple chemical transformations, i.e. methylation and (de)protonation of the [3]rotaxane and [2]catenane allowed controllable transformations within the conformationally flexible calix[4]phyrin-incorporated mechanically interlocked porphyrinoids.

Integrating Molecular Motions in Ternary Cocrystals for NIR-II Photothermal Conversion

Organic photothermal conversion materials hold immense promise for various applications owing to their structural flexibility. Recent research has focused on enhancing near-infrared (NIR) absorption and mitigating radiative transition processes. In this study, we have developed a viable approach to the design of photothermal conversion materials through the construction of ternary organic cocrystals, by introducing a third component as a molecular blocker and motion unit into a binary donor-acceptor system. Superstructural and photophysical properties of the ternary cocrystals were characterized using various spectroscopic techniques. The role of the molecular blocker in radical stabilization and photothermal conversion was demonstrated. Intriguingly, the motions of the entire pyrene molecules in the cocrystal have been observed by the results of variable temperature single-crystal X-ray diffraction. The excellent performance of the ternary cocrystal as a photothermal material was validated through efficient NIR-II photothermal and solar-driven water evaporation experiments. The efficiency of water evaporation reached 88.7 %, with a corresponding evaporation rate of 1.29 kg m-2 h-1, representing excellent performance among pure organic small molecular photothermal conversion materials. Our research underscores the introduction of molecular blockers and motion units to stabilize radicals and produce outstanding photothermal conversion materials, offering new pathways for developing efficient and stable photothermal conversion materials.

Chiral Induction of a Tetrakis(porphyrin) in Various Chiral Solvents

Non-covalent interactions offer an alternative way for developing stimulus-responsive materials such as sensors, machines, and drug-delivery systems. We recently reported that a urethane-equipped tetrakis(porphyrin) forms one-handed helical supramolecular polymers in solution in response to chirality of chiral solvents. Conformational changes in helical sense were detected using circular dichroism (CD) spectroscopy, which showed that the tetrakis(porphyrin) can possibly be used as a sensor for determining the enantiomeric excess of a chiral analyte. Hence, we studied the scope and limitations of the chiral-induction behavior of tetrakis(porphyrin) to deepen the understanding of tetrakis(porphyrin)-based chiral sensing systems. Herein, we report the chiral-induction behavior of tetrakis(porphyrin) in various chiral solvents, which was found to be CD-active in many chiral solvents. Notably, the tetrakis(porphyrin) was CD active in a cryptochiral molecular solvent, which is exciting because the chiralities of acyclic saturated hydrocarbons are hard to sense. Consequently, this study highlights the potential advantages of supramolecular chiral sensors capable of targeting a wide range of analytes, including molecules that are absorption-silent in the UV/vis region, ones devoid of anchoring functional groups, and acyclic, saturated hydrocarbons.

Wiring proton gradients for energy conversion

Light-switchable buffer solutions based on merocyanine photoacids can be used as efficient photoenergy harvesting systems. Varying the solvation environment of merocyanine photoacids in water-methanol mixtures allows one to carefully tune their photoacidity, relaxation kinetics, and solubility, opening up the possibility to install persistent pH gradients of approximately 4 pH units under 500 nm light. When interfaced between two electrodes and exposed to asymmetric light irradiation, these solutions can be photoactivated precisely both in space and time, generating open circuit voltages as high as 240 mV that can last hours under steady-state irradiation - an outcome that is akin the peak performance of biological transmembrane proton pumps.

Multivariate Flexible Metal-Organic Frameworks and Covalent Organic Frameworks

Precise control of the void environment, achieved through multiple functional groups and enhanced by structural adaptations to guest molecules, stands at the forefront of scientific inquiry. Flexible multivariate open framework materials (OFMs), including covalent organic frameworks and metal-organic frameworks, meet these criteria and are expected to play a crucial role in gas storage and separation, pollutant removal, and catalysis. Nevertheless, there is a notable lack of critical evaluation of achievements in their chemistry and future prospects for their development or implementation. To provide a comprehensive historical context, the initial discussion explores into the realm of "classical" flexible OFMs, where their origin, various modes of flexibility, similarities to proteins, advanced tuning methods, and recent applications are explored. Subsequently, multivariate flexible materials, the methodologies involved in their synthesis, and horizons of their application are focussed. Furthermore, the reader to the concept of spatial distribution is introduced, providing a brief overview of the latest reports that have contributed to its elucidation. In summary, the critical review not only explores the landscape of multivariate flexible materials but also sheds light on the obstacles that the scientific community must overcome to fully unlock the potential of this fascinating field.

Formation and Stability of Benzylic Amide [2]- and [3]Rotaxanes: An Intercomponent Interactions Study

One of the most recent focuses in supramolecular chemistry is developing molecules designed to exhibit programmable properties at the molecular level. Rotaxanes, which function as molecular machines with movements controlled by external stimuli, are prime candidates for this purpose. However, the controlled synthesis of rotaxanes, especially amide-benzylic rotaxanes with more than two components, remains an area ripe for exploration. In this study, we aim to elucidate the formation of amide-benzylic [3]rotaxanes using a thread that includes a conventional succinamide station and an innovative triazole-carbonyl station. Including the triazole-carbonyl station introduces new perspectives into the chemistry of rotaxanes, influencing their conformation and dynamics. The synthesis of two-station rotaxanes with varying stoppers demonstrated that the macrocycle consistently occupies the succinamide station, providing greater stability as evidenced by NMR and SC-XRD analyses. The presence of a triazole-carbonyl station facilitated the formation of a second macrocycle exclusively when a secondary amide was employed as the stopper group, presumably due to decreased steric hindrance. Moreover, the second macrocycle directly forms at the triazole-carbonyl station. This investigation reveals that slight modifications in the thread structure can dramatically impact the formation, stability, and interactions between components of rotaxanes.

Photoinduced Isomerization of [N2]2- in a Bimetallic Lutetium Complex

The first lanthanide dinitrogen photoswitch [(C5Me4H)2(THF)Lu]2(μ-η2:η2-N2), 1, is reported. 1 is a unique example of controlled isomerization between side-on and end-on coordination modes of [N2]2- in a bimetallic lutetium dinitrogen complex that results in photochromism. Near-infrared light (NIR) was used to promote this effect, as evidenced by single X-ray diffraction (XRD) connectivity and Raman data, generating the [N2]2- end-on bound isomer, [(C5Me4H)2(THF)Lu]2(μ-η1:η1-N2), 2. Although different ligands and coordinating solvents were studied to replicate and control the optical properties in 1/2, only the original configuration with C5Me4H ligands and THF as the coordinating solvent worked. Supported by the first-principles calculations, the electronic structures along with the mechanistic details of the side-on to end-on isomerization were unraveled. Preliminary reactivity studies show that 2 formed with NIR light reacts with anthracene, generating dihydroanthracene and anthracene dimers, indicating new redox reaction pathways.

Molecular-scale dissipative chemistry drives the formation of nanoscale assemblies and their macroscale transport

Fuelled chemical systems have considerable functional potential that remains largely unexplored. Here we report an approach to transient amide bond formation and use it to harness chemical energy and convert it to mechanical motion by integrating dissipative self-assembly and the Marangoni effect in a source-sink system. Droplets are formed through dissipative self-assembly following the reaction of octylamine with 2,3-dimethylmaleic anhydride. The resulting amides are hydrolytically labile, making the droplets transient, which enables them to act as a source of octylamine. A sink for octylamine was created by placing a drop of oleic acid at the air-water interface. This source-sink system sets up a gradient in surface tension, which gives rise to a macroscopic Marangoni flow that can transport the droplets in solution with tunable speed. Carbodiimides can fuel this motion by converting diacid waste back to anhydride. This study shows how fuelling at the molecular level can, via assembly at the supramolecular level, lead to liquid flow at the macroscopic level.

Supramolecular and molecular capsules, cages and containers

Stemming from early seminal notions of molecular recognition and encapsulation, three-dimensional, cavity-containing capsular compounds and assemblies have attracted intense interest due to the ability to modulate chemical and physical properties of species encapsulated within these confined spaces compared to bulk environments. With such a diverse range of covalent motifs and non-covalent (supramolecular) interactions available to assemble building blocks, an incredibly wide-range of capsular-type architectures have been developed. Furthermore, synthetic tunability of the internal environments gives chemists the opportunity to engineer systems for uses in sensing, sequestration, catalysis and transport of molecules, just to name a few. In this tutorial review, an overview is provided into the design principles, synthesis, characterisation, structural facets and properties of coordination cages, porous organic cages, supramolecular capsules, foldamers and mechanically interlocked molecules. Using seminal and recent examples, the advantages and limitations of each system are explored, highlighting their application in various tasks and functions.

Path-Independent All-Visible Orthogonal Photoswitching for Applications in Multi-Photochromic Polymers and Molecular Computing

Synthetic molecular photoswitches have taken center stage as high-precision tools to introduce light-responsiveness at the smallest scales. Today they are found in all areas of applied chemistry, covering materials research, chemical biology, catalysis, or nanotechnology. For a next step of applicability truly orthogonal photoswitching is highly desirable but to date such independent addressability of different photoswitches remains highly challenging. Herein we present the first example of all-visible, all-light responsive, and path- independent orthogonal photoswitching. By combining two recently developed indigoid photoswitches - peri-anthracenethioindigo and a rhodanine-based chromophore - a four-state system is established and each state can be accessed in high yields completely independently and also with visible light irradiation only. The four states give rise to four different colors, which can be transferred to a solid polymer matrix to yield a versatile multi-state photochromic material. Further, combination with a fluorescent dye as a third component is possible, demonstrating the applicability of this orthogonal photoswitching system in all-photonic molecular logic behavior and information processing.

Acid/base responsive pseudo[3]rotaxanes from amine naphthotubes and bis-pyridinium/isoquinolinium guests

A novel cooperative pseudo[3]rotaxane system was successfully constructed by the inclusion complexation of two identical amine naphthotubes with a bis-pyridinium/isoquinolinium guest. Single crystal structure analysis revealed that weak Csp3-H⋯O hydrogen bonds between the two hosts are responsible for the positive cooperativity during the formation of pseudo[3]rotaxanes. Moreover, intermolecular charge-transfer interactions between the electron-rich host and the electron-poor guests were observed. The pseudo[3]rotaxanes showed pH-controllable association/dissociation processes with naked-eye color changes in solution.

Insight from Electrochemical Analysis in the Radical Cation State of a Monopyrrolotetrathiafulvalene-Based [2]Rotaxane

Mechanically interlocked molecules are a class of compounds used for controlling directional movement when barriers can be raised and lowered using external stimuli. Applied voltages can turn on redox states to alter electrostatic barriers but their use for directing motion requires knowledge of their impact on the kinetics. Herein, we make the first measurements on the movement of cyclobis(paraquat-p-phenylene) (CBPQT4+) across the radical-cation state of monopyrrolotetrathiafulvalene (MPTTF) in a [2]rotaxane using variable scan-rate electrochemistry. The [2]rotaxane is designed in a way that directs CBPQT4+ to a high-energy co-conformation upon oxidation of MPTTF to either the radical cation (MPTTF⋅+) or the dication (MPTTF2+). 1H NMR spectroscopic investigations carried out in acetonitrile at 298 K showed direct interconversion to the thermodynamically more stable ground-state co-conformation with CBPQT4+ moving across the oxidized MPTTF2+ electrostatic barrier. The electrochemical studies revealed that interconversion takes place by movement of CBPQT4+ across both the MPTTF•+ (19.3 kcal mol-1) and MPTTF2+ (18.7 kcal mol-1) barriers. The outcome of our studies shows that MPTTF has three accessible redox states that can be used to kinetically control the movement of the ring component in mechanically interlocked molecules.

Non-equilibrium self-assembly for living matter-like properties

The soft and wet machines of life emerged as the spatially enclosed ensemble of biomolecules with replicating capabilities integrated with metabolic reaction cycles that operate at far-from-equilibrium. A thorough step-by-step synthetic integration of these elements, namely metabolic and replicative properties all confined and operating far-from-equilibrium, can set the stage from which we can ask questions related to the construction of chemical-based evolving systems with living matter-like properties - a monumental endeavour of systems chemistry. The overarching concept of this Review maps the discoveries on this possible integration of reaction networks, self-reproduction and compartmentalization under non-equilibrium conditions. We deconvolute the events of reaction networks and transient compartmentalization and extend the discussion towards self-reproducing systems that can be sustained under non-equilibrium conditions. Although enormous challenges lie ahead in terms of molecular diversity, information transfer, adaptation and selection that are required for open-ended evolution, emerging strategies to generate minimal metabolic cycles can extend our growing understanding of the chemical emergence of the biosphere of Earth.

Mix and Match Tuning of the Conformational and Multistate Redox Switching Properties of an Overcrowded Alkene

Overcrowded alkenes have received considerable attention as versatile structural motifs in a range of optical switches and light-driven unidirectional motors. In contrast, their actuation by electrochemical stimuli remains underexplored, even though this alternative energy input may be preferred in various applications and enables additional control over molecular switching states and properties. While symmetric bistricyclic overcrowded enes (BAEs) containing two identical halves based on either thioxanthene (TX) or acridine (Acr) motifs are known to be reversible conformational redox switches, their redox potentials are generally too high or low, respectively, thereby preventing wider applications. Herein, we demonstrate that the "mixed" TX-Acr switch possesses redox properties that lie between those of its parent symmetric analogs, enabling interconversion between three stable redox and conformational states at mild potentials. This includes the neutral anti-folded, the dicationic orthogonal, and a unique twisted monoradical cation state, the latter of which is only accessible in the case of the mixed TX-Acr switch and in a pathway-dependent manner. Consequently, with this multistate redox switch, a myriad of molecular properties, including geometry, polarity, absorbance, and fluorescence, can be modulated with high fidelity and reversibility between three distinct stable states. More generally, this study highlights the versatility of the "mix and match" approach in rationally designing redox switches with specific (redox) properties, which in turn is expected to enable a myriad of applications ranging from molecular logic and memory to actuators and energy storage systems.

Photoisomerization mechanism of iminoguanidinium receptors from spectroscopic methods and quantum chemical calculations

The hydrazone functional group, when coupled with a pyridyl substituent, offers a unique class of widely tunable photoswitches, whose E-to-Z photoisomerization equilibria can be controlled through intramolecular hydrogen bonding between the N-H hydrazone donor and the pyridyl acceptor. However, little is known about the photoisomerization mechanism in this class of compounds. To address this issue, we report a pyridine-appended iminoguanidinium photoswitch that is functionally related to acylhydrazones and provides insight into the photoisomerization processes between the E and Z configurations. The E-to-Z photoisomerization of the E-2-pyridyl-iminoguanidinium cation (2PyMIG) in DMSO, prepared as the bromide salt, was quantified by 1H NMR, and probed in real time with ultrafast laser spectroscopy. The photoisomerization process occurs on a picosecond timescale, resulting in low fluorescence yields. The multiconfigurational reaction path found with the growing string method features a small barrier (4.3 or 6.5 kcal mol-1) that the E isomer in the π-π* state must overcome to reach the minimum energy conical intersection (MECI) connecting the E and Z isomers of 2PyMIG. While two possible pathways exist depending on the orientation of the pyridine ring, both exhibit the same qualitative features along the path and at their MECIs, involving simultaneous changes in the CCNN and CNNC dihedral angles. Furthermore, the ground state barrier for pyridine ring rotation is readily accessible, thus a low barrier pathway to the experimentally observed Z isomer exists for both MECIs leading to a transition from the E isomer to photoproduct. Combining multiconfigurational reaction path calculations using growing string method with time-resolved fluorescence spectroscopy provided crucial insights into the photoisomerization process of 2PyMIG, resulting in both the computational and experimental results pointing to rapid photoisomerization via a surface crossing between the singlet π-π* and the ground states.

Directional Bias in Molecular Photogearing Evidenced by LED-Coupled Chiral Cryo-HPLC

Molecular gearing systems are technomimetic nanoscale analogues to complex geared machinery in the macroscopic world. They are defined as systems incorporating intermeshed movable parts which perform correlated rotational motions by mechanical engagement. Only recently, new methods to actively drive molecular gearing motions instead of relying on passive thermal activation have been developed. Further progress in this endeavor will pave the way for unidirectional molecular gearing devices with a distinct type of molecular machine awaiting its realization. Within this work an essential step towards this goal is achieved by evidencing directional biases for the light-induced rotations in our molecular photogear system. Using a custom-designed LED-coupled chiral cryo-HPLC setup for the in situ irradiation of enantiomeric analytes, an intrinsic selectivity for clockwise or counterclockwise rotations was elucidated experimentally. Significant directional biases in the photogearing processes and light-induced single bond rotations (SBRs) are observed for our photogear with directional preferences of up to 4.8 : 1. Harnessing these effects will allow to rationally design and construct a fully directional molecular gearing motor in the future.

Cascading Macrocycle and Helix Motions in a Foldarotaxane Molecular Shuttle

The design of a dynamically assembled foldarotaxane was envisioned with the aim of operating as a two cascading trigger-based molecular shuttle. Under acidic conditions, both the macrocycle and helix were localized around their respective best molecular stations because they are far enough from each other not to alter the stability of complexes. The pH-dependent localization of the macrocycle along the encircled axle allowed us to modulate the association between the helical foldamer and its sites of interaction on the axle. Under kinetic control-at low concentration and room temperature-when the foldarotaxane supramolecular architecture is kinetically stable, the pH-responsive translation of the macrocycle along the thread triggered the gliding of the helix away from its initial best station. At higher concentration-when helix assembly/disassembly process is accelerated-the system reached the equilibrium state. A new foldarotaxane isomer then appeared through the change of the relative position of the helix and macrocycle along the thread. In this isomer, the helix segregated the macrocycle away from its best station. The fine control of the kinetic and thermodynamic processes, combined with the control of pH, allowed the reciprocal segregation of the helix or the ring away from their respective best sites of interaction.

Light-Powered Propeller-like Transporter for Boosted Transmembrane Ion Transport

Membrane-active molecular machines represent a recently emerging, yet important line of expansion in the field of artificial transmembrane transporters. Their hitherto demonstrated limited types (molecular swing, ion fishers, shuttlers, rotors, etc.) certainly call for new inspiring developments. Here, we report a very first motorized ion-transporting carrier-type transporter, i.e., a modularly tunable, light-powered propeller-like transporter derived from Feringa's molecular motor for consistently boosting transmembrane ion transport under continuous UV light irradiation. Based on the EC50 values, the molecular propeller-mediated ion transport activities under UV light irradiation for 300 s are 2.31, 1.74, 2.29, 2.80, and 2.92 times those values obtained without irradiation for Li+, Na+, K+, Rb+, and Cs+ ions, respectively, with EC50 value as low as 0.71 mol % for K+ ion under light irradiation.

Directionality Reversal and Shift of Rotational Axis in a Hemithioindigo Macrocyclic Molecular Motor

Molecular motors are central driving units for nanomachinery, and control of their directional motions is of fundamental importance for their functions. Light-driven variants use easy to provide, easy to dose, and waste-free fuel with high energy content, making them particularly interesting for applications. Typically, light-driven molecular motors work via rotations around dedicated chemical bonds where the directionality of the rotation is dictated by the steric effects of asymmetry in close vicinity to the rotation axis. In this work, we show how unidirectional rotation around a virtual axis can be realized by reprogramming a molecular motor. To this end, a classical light-driven motor is restricted by macrocyclization, and its intrinsic directional rotation is transformed into a directional rotation of the macrocyclic chain in the opposite direction. Further, solvent polarity changes allow to toggle the function of this molecular machine between a directional motor and a nondirectional photoswitch. In this way, a new concept for the design of molecular motors is delivered together with elaborate control over their motions and functions by simple solvent changes. The possibility of sensing the environmental polarity and correspondingly adjusting the directionality of motions opens up a next level of control and responsiveness to light-driven nanoscopic motors.

On the supramolecular interactions into a pH- and Metal-Actuated Molecular Shuttle: some insights from QTAIM modeling

Supramolecular contacts responsible for chemical interaction of cucurbit[7]uril (CB[7]) macrocycle on a Tolyl-Viologen-Phenylene-Imidazole (T-VPI) molecular thread, at acid pH (T-VPI-H+) or after Ag+ cation addition (T-VPI-Ag+), are analytically addressed in a computational framework combining Quantum Theory of Atoms in Molecules (QTAIM) with Density Functional Theory (DFT). In this respect, the crystallographic structure (CCDC number 2217466) is taken as reference condition for addressing the nature of the chemical interactions driving the shuttling of the CB[7] between T and P stations recently observed in dilute water solutions. Beside the host(CB[7]) vs guest(T-VPI-H+ or T-VPI-Ag+) complexation, the coordination sphere of the Ag+ cation is also investigated by means of local electronic energy density - H(r) - descriptors. The derived non-covalent interaction patterns are found to support diagnostic 1H NMR signals used for detecting the mutual position of the CB[7] along the axle. This work highlights the potentialities of a QTAIM based approach in the characterization of supramolecular and metal-complexation effects in molecular aggregates such as not-interlocked synthetic molecular shuttles.

Proton Conduction in Chiral Molecular Assemblies of Azolium-Camphorsulfonate Salts

Chiral molecular assemblies have attracted considerable attention because of their interesting physical properties, such as spin-selective electron transport. Cation-anion salts of three azolium cations, imidazolium (HIm+), triazolium (HTrz+), and thiazolium (HThz+), in combination with a chiral camphorsulfonate (1S-CS-) and their racemic compounds (rac-CS-) were prepared and compared in terms of phase transitions, crystal structures, dynamics of constituent molecules, dielectric responses, and proton conductivities. The cation-anion crystals containing HIm+ showed no significant difference in proton conductivity between the homochiral and racemic crystals, whereas the HTrz+-containing crystals showed higher proton conductivity and lower activation energy in the homochiral form than in the racemic form. A two-dimensional hydrogen-bonding network consisting of HTrz+ and -SO3- groups and similar in-plane rotational motion was observed in both crystals; however, the HTrz+ cation in the homochiral crystal exhibited the rotational motion modulated with translational motion, whereas the HTrz+ cation in the racemic crystal exhibited almost steady in-plane rotational motion. The different motional degrees of freedom were confirmed by crystal structure analyses and temperature- and frequency-dependent dielectric constants. In contrast, steady in-plane rotational motion with the thermally activated fluctuating motion of CS- was observed both in homochiral and racemic crystals containing HIm+, which averaged the motional space of protons resulting in similar dielectric responses and proton conductivities. The control of motional degrees of freedom in homochiral crystals affects the proton conductivity and is useful for the design of molecular proton conductors.

Controlled interconversion of macrocyclic atropisomers via defined intermediates

Macrocyclic conformations play a crucial role in regulating their properties. Our understanding of the determinants to control macrocyclic conformation interconversion is still in its infancy. Here we present a macrocycle, octamethyl cyclo[4](1,3-(4,6)-dimethylbenzene)[4]((4,6-benzene)(1,3-dicarboxylate) (OC-4), that can exist at 298 K as two stable atropisomers with C2v and C4v symmetry denoted as C2v-OC-4 and C4v-OC-4, respectively. Heating induces the efficient stepwise conversion of C2v- to C4v-OC-4 via a Cs-symmetric intermediate (Cs-OC-4). It differs from the typical transition state-mediated processes of simple C-C single bond rotations. Hydrolysis and further esterification with a countercation dependence promote the generation of C2v- and Cs-OC-4 from C4v-OC-4. In contrast to C2v-OC-4, C4v-OC-4 can bind linear guests to form pseudo-rotaxans, or bind C60 or C70 efficiently. The present study highlights the differences in recognition behavior that can result from conformational interconversion, as well as providing insights into the basic parameters that govern coupled molecular rotations.

Formylation boosts the performance of light-driven overcrowded alkene-derived rotary molecular motors

Artificial molecular motors and machines constitute a critical element in the transition from individual molecular motion to the creation of collective dynamic molecular systems and responsive materials. The design of artificial light-driven molecular motors operating with high efficiency and selectivity constitutes an ongoing fundamental challenge. Here we present a highly versatile synthetic approach based on Rieche formylation that boosts the quantum yield of the forward photoisomerization reaction while reaching near-perfect selectivity in the steps involved in the unidirectional rotary cycle and drastically reducing competing photoreactions. This motor is readily accessible in its enantiopure form and operates with nearly quantitative photoconversions. It can easily be functionalized further and outperforms its direct predecessor as a reconfigurable chiral dopant in cholesteric liquid crystal materials.

Photoswitchable Imines Drive Dynamic Covalent Systems to Nonequilibrium Steady States

Coupling a photochemical reaction to a thermal exchange process can drive the latter to a nonequilibrium steady state (NESS) under photoirradiation. Typically, systems use separate motifs for photoresponse and equilibrium-related processes. Here, we show that photoswitchable imines can fulfill both roles simultaneously, autonomously driving a dynamic covalent system into a NESS under continuous light irradiation. We demonstrate this using transimination reactions, where E-to-Z photoisomerism generates a more kinetically labile species. At the NESS, energy is stored both in the metastable Z-isomer of the imine and in the system's nonequilibrium constitution; when the light is switched off, this stored energy is released as the system reverts to its equilibrium state. The system operates autonomously under continuous light irradiation and exhibits characteristics of a light-driven information ratchet. This is enabled by the dual-role of the imine linkage as both the photochromic and dynamic covalent bond. This work highlights the ability and application of these imines to drive systems to NESSs, thus offering a novel approach in the field of systems chemistry.

Redox-Switchable Aromaticity in a Helically Extended Indeno[2,1-c]fluorene

Molecular switches have received major attention to enable the reversible modulation of various molecular properties and have been extensively used as trigger elements in diverse fields, including molecular machines, responsive materials, and photopharmacology. Antiaromaticity is a fascinating property that has attracted not only significant fundamental interest but is also increasingly relevant in different applications, in particular organic (opto)electronics. However, designing systems in which (anti)aromaticity can be judiciously and reversibly switched ON and OFF remains challenging. Herein, we report a helicene featuring an indenofluorene-bridged bisthioxanthylidene as a novel switch wherein a simultaneous two-electron (electro)chemical redox process allows highly reversible modulation of its (anti)aromatic character. Specifically, the two thioxanthylidene rotors, attached to the initially aromatic indenofluorene scaffold via overcrowded alkenes, adopt an anti-folded structure, which upon oxidation convert to singly bonded, twisted conformations. This is not only associated with significant (chir)optical changes but importantly also results in formation of the fully conjugated, formally antiaromatic as-indacene motif in the helical core of the switch. This process proceeds without the buildup of radical cation intermediates and thus enables highly reversible switching of molecular geometry, aromaticity, absorbance, and chiral expression under ambient conditions, as evidenced by NMR, UV-vis, CD, and (spectro)electrochemical analyses, supported by DFT calculations. We expect this concept to be extendable to a wide range of robust antiaromatic-aromatic switches and to provide a basis for modulation of the structure and properties of these fascinating inherently chiral polycyclic π-scaffolds.

Supramolecular assemblies of amphiphilic donor-acceptor Stenhouse adducts as macroscopic soft scaffolds

In the design of photoharvesting and photoresponsive supramolecular systems in aqueous medium, the fabrication of amphiphilic photoswitches enables a noninvasive functional response through photoirradiation. Although most aqueous supramolecular assemblies are driven by high-energy and biodamaging UV light, we have previously reported a design of amphiphilic donor-acceptor Stenhouse adducts (DASAs) controlled by white light. Herein, we present a series of DASA amphiphiles (DAs) with minor structural modifications on the alkyl linker chain length connecting the DASA motif with the hydrophilic moiety. The excellent photoswitchability in organic medium and the photoresponsiveness in aqueous medium, driven by visible light, were investigated by UV-vis absorption spectroscopy. The assembled supramolecular nanostructures were confirmed by electron microscopy, while the supramolecular packing was revealed by X-ray diffraction analysis. Upon visible-light irradiation, significant transformations of the DA geometry enabled transformations of the supramolecular assemblies on a microscopic scale, subsequently disassembling macroscopic soft scaffolds of DAs. The current work shows promising use for the fabrication of visible-light-controlled macroscopic scaffolds, offering the next generation of biomedical materials with visible-light-controlled microenvironments and future soft-robotic systems.